1. Field of the Invention
The present invention relates generally to a thermoelectric power apparatus to generate electric power utilizing the Seebeck effect. More particularly, the present invention relates to a thermoelectric power apparatus and method for optimally generating electric power according to a temperature variation and a temperature distribution of a heat source, and to an apparatus and method for avoiding a reduction of generated electric power due to wire breakage so as to secure long life and high reliability.
2. Description of the Related Art
Various thermoelectric power generating apparatuses have been proposed to generate electric power utilizing the Seebeck effect. A thermoelectromotive force generated due to the Seebeck effect is dependent upon a temperature difference between a high-temperature heat source and a low-temperature heat source. Hence, output voltages of the previously proposed thermoelectric power generating apparatuses tend to fluctuate. That is to say, the output voltages normally lower from a desired voltage or remarkably increase in comparison with the desired voltage according to the temperature variation and the temperature distribution of the heat source.
To cope with such a fluctuation in the output voltage as described above, it has been proposed to utilize a plurality of thermoelectric modules, each thermoelectric module having a plurality of couples of thermoelectric devices which are connected to one another. An electrical connection of these thermoelectric modules is switched from a series connection to a parallel connection and vice versa to generate electric power according to a load.
One example of a thermoelectric power generating apparatus utilizing the above-described technique of switching the connection form of the plurality of thermoelectric modules between a series connection and a parallel connection is disclosed in a Japanese Patent Application First Publication No. Heisei 8-37322, published on Feb. 6, 1996. In that Japanese Patent Application First Publication, a thermoelectric power generating apparatus is applied to an electric cell for a watch. The switching of the connection form of the plurality of thermoelectric modules is performed on the basis of the output voltage of a particular thermoelectric module from among the plurality of thermoelectric modules, and electric power is supplied to electric charging means, such as a secondary electric cell.
On the other hand, since the electromotive force generated utilizing the Seebeck effect is generally small, it is necessary to connect several thermoelectric devices in series to obtain a large amount of electric power. For example, in a thermoelectric power generating apparatus that generates electric power as large as several watts through several hundred kilowatts, a relatively high temperature heat source such as an incinerator's heat or exhaust gas heat from an automotive vehicle is used. In such cases, however, reliability is reduced due to electrical line (wire) breakage.
To increase the reliability of the thermoelectric power generating apparatus as described above, it has been proposed to use a technique in which the occurrence of electrical line (wire) breakage of the devices constituting the thermoelectric power generating apparatus or of the thermoelectric modules is detected so as not to adversely affect functions of normal devices or normal thermoelectric modules. One example of this technique is disclosed in Japanese Patent Application First Publication No. Heisei 8-32125 published on Feb. 2, 1996. In this Japanese Patent Application First Publication, such a method is disclosed wherein the thermoelectric devices in each thermoelectric module are divided into a plurality of blocks. The occurrence of the electrical wire (line) breakage is detected, and any one or more of the blocks in which the occurrence of the line breakage is detected are electrically bypassed through a bypass circuit arranged in parallel to each block.
However, in the thermoelectric power generating apparatuses disclosed in Japanese Patent Application Publication No. Heisei 8-37322, the switching of the connection form between a serial connection and a parallel connection on the basis of the output voltage of the particular thermoelectric module is carried out. In a case where any line in the particular thermoelectric module is broken and the output voltage has failed, the electric charging cannot be made completely,
In the line breakage detecting method disclosed in Japanese Patent Application First Publication Heisei 8-32125, an external power supply is connected to a series circuit constituted by the thermoelectric module and a comparison (pull down) resistor. As a result, a current is caused to pass through the series circuit, a voltage comparison is made between a voltage drop in the thermoelectric module and a reference voltage is used to detect whether the line breakage occurs in the thermoelectric module. Hence, it is impossible to accurately determine the line breakage while the voltage (the thermoelectromotive force) is generated in the thermoelectric module. That is to say, while the voltage is generated, the occurrence of a line breakage cannot be detected. If the line breakage has occurred during the operation of the thermoelectric module, the generation of the thermoelectric force cannot completely be advanced. In addition, an external power supply is used. Hence, a cost of manufacturing such thermoelectric module as described in the latter Japanese Patent Application Publication is increased. Power generation cannot be made any more while the determination of whether the line breakage occurs is carried out. Further, the algorithm for line breakage determination is complex and is time consuming. Consequently, efficiency of power generation is reduced.